Chapter 2 - The Chemical Context of Life

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any substance that can't be broken down to any other substance by chemical reactions

compound

a substance consisting of two or more different elements combined in a fixed ratio

essential element

essential for life (for plants life cycle) can be in big and small amounts

trace element

element indispensable for life but required in extremely minute amounts

neutron

a subatomic particle having no electrical charge (electrically neutral) 1.7x10-24 g in nucleus

proton

a subatomic particle with a single positive charge, 1.7x10-24 g in nucleus

electron

a subatomic particle with a single negative charge & a mass of about 1/2000 that of a neutron/proton, on or more move around the nucleus of an atom

atomic number

the number of protons in the nucleus of an atom, unique for each element & designated by a superscript to the left of the element symbol

atomic mass

the total mass of an atom, which is the mass in grams of one mole of the atom

isotope

one of the several atomic forms of an element, each with the same number of protons but a different number of neutrons, thus differing in atomic mass

electron shells

an energy level of electrons at a characteristic average distance from the nucleus of an atom

energy

the capacity to cause change, especially to do work (to move matter against an opposing force)

potential energy

energy that matter possesses as a direct result of its location or spatial arrangement (structure)

molecule

two or more atoms held together by a covalent bond

double bond

the sharing of two pairs of valence electrons by two atoms

electronegativity

the attraction of a given atom for the electrons of a covalent bond, some have stronger pull than others

nonpolar covalent bond

one in which electrons are shared equally between to atoms of similar electronegativity, such as O2 or H2

polar covalent bond

one between atoms that differ in electronegativity, the shared electrons are pulled closer to the more elctronegative atom, making it slightly negative and the other atom slightly positive

anion

a negatively charged ion

cation

a positively charged ion

hydrogen bond

a type of weak chemical bond that is formed when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule

van der Waals interactions

weak attractions between molecules or parts of molecules that result from localized charge fluctuations, they occur only when atoms and molecules are very close together

dynamic equilibrium

the state in which the rate of the forward reaction equals the rate of the reverse reaction, so that the relative concentrations of the reactants and products don't change with time, it only implies that their concentrations have stabilized at a particular ration